Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
1995 Geo Prizm Base, AutomaticFACTORY OEM SERVICE PROCEDURE
Engine Controls DTCS (1.8L)
ENGINE CONTROLS DTCS (1.8L)
| OEM Code | Description |
|---|---|
| 12 | NO RPM SIGNAL |
| 13 | NO RPM SIGNAL |
| 14 | NO IGNITION SIGNAL |
| 16 | PCM CONTROL SIGNAL FAILURE |
| 21 | (CALIF EMISSIONS) O2 SENSOR CIRCUIT, OPEN OR SHORTED CIRCUIT |
| 21 | (FEDERAL EMISSIONS) O2S, OPEN OR SHORTED CIRCUIT |
| 22 | ENGINE COOLANT TEMP ECT SENSOR, OPEN OR SHORTED CKT |
| 24 | IAT SENSOR, OPEN OR SHORTED CIRCUIT |
| 25 | (CALIFORNIA EMISSIONS) O2S, AIR/FUEL RATIO LEAN |
| 25 | (FEDERAL EMISSIONS) O2S, AIR/FUEL RATIO LEAN |
| 26 | (CALIFORNIA EMISSIONS) O2S, AIR/FUEL RATIO RICH |
| 26 | (FEDERAL EMISSIONS) O2S, AIR/FUEL RATIO RICH |
| 27 | (CALIF EMISSIONS) SUB-HEATED O2 SENSOR (SUB-HO2S), OPEN OR SHORTED CIRCUIT |
| 27 | (FEDERAL EMISSIONS) SUB-O2 SENSOR (SUB-O2S), OPEN OR SHORTED CIRCUIT |
| 31 | MAP SENSOR, OPEN OR SHORTED CIRCUIT |
| 41 | TP SENSOR, OPEN OR SHORTED CIRCUIT |
| 42 | VEHICLE SPEED SENSOR, OPEN OR SHORTED CIRCUIT |
| 43 | NO CRANK SIGNAL |
| 51 | SWITCH CONDITION SIGNAL |
| 52 | KNOCK SENSOR (KS), OPEN OR SHORTED CIRCUIT |
| 71 | EXHAUST GAS RECIRCULATION (EGR) SYSTEM |
Factory Service Tools
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.
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